"Last Battle" is fittingly enough, a song from the last battle of Xenosaga: Episode I. Most final boss themes are known to be grand, bombastic, epic, threatening, etc. This isn't one of those kinda themes. "Last Battle" opens up calmly with the duo of piano and violin. There is a quickly established sense of unease however in in how quickly repeated the violin melody is, and how the 6/4 time accentuates this. As the track continues, a bit of vocal chanting is inserted and then after about 40 seconds a drum track comes into the mix.
If the song wasn't unsettling enough at this point, the drumming has an odd syncopation to it; that is it stresses odd notes that you wouldn't traditionally find stress on. If you're not sure what that means, try tapping along to the drum beat. You'll likely find that the snare drum in the song hits at a time you don't expect it to until you listen to the rhythm for a while.
There is a more piano-centric breakdown to the song that softens the tone and drops the drums, but then comes right back into the main melody with full force.
When compared to other final boss themes, "Last Battle" is surprisingly understated. It relies more on its time signature, percussion, and limited instrumentation to create a unique atmosphere rather than bombast and power.